Osmium coating is suitable for SEM and TEM observation. This is a concept for the deposition of fine structureless and featureless thin film coatings on surfaces for applications in electron microscopy, especially for those who are using a FESEM.
A metallization coating is not just to reduce or eliminate charging, it is also helpful to impart to the image enhanced contrast. So even when conductivity is not an issue, the osmium coating can play a role in the development of contrast in an unknown image.
Notice: as osmium is dangerous, this coating is applied when there is no other suitable coating method.